Troponin I, slow skeletal muscle, also known as TNNI1, belongs to the troponin I family. TNNI1 is the inhibitory subunit of troponin, the thin filament regulatory complex which confers calcium-sensitivity to striated muscle actomyosin ATPase activity. Recombinant human TNNI1 protein, fused to His-tag at N-terminus, was expressed in E.coli.